David skinner, age 13, of Allentown, pa., for his question:
Haw does the milky way revo1ve?
On a clear night, the milky way arches over the heavens like a wispy haze. We are only just beginning to learn that the beautiful ghostly glimmer is far more wonderful than it appears to be. We must stretch our minds to grasp its tremendous size and exercise our imaginations to realize the orderly system of its billions of stars.
The vast system of stars we call the milky way rotates around its axis somewhat like a monstrous pinwheel. In order to imagine its rotation, we must have an idea of its shape and allocate it some directions to know which way it is turning. Our earth, of course, is part of the whirling system, and every star, every speck of debris in the milky way is also moving.
Astronomers can take telescopic photographs of sections of the milky way and assemble them to give an over all picture. The hazy glow is broken here and there with streaks and dark patches, but the general shape is like a lens. Our view is edgewise across the vast system, and the ghostly glimmer of the milky way is actually the light from billions of distant stars.
The big wheel is thickest at the hub, where the stars are most dense. This is where we start t0 give directions to the starry system. We imagine a line from top to bottom through the hub of the milky way. This is the axis around, which it rotates, and we place the poles one at each end of the axis. The equator of the milky
Way is half way between the two poles, around the wide rim of the spinning wheel of stars.
The swarming stars at the hub of the milky way rotate fastest, and the streaming lanes of traffic get slrnter out near the slim rim of the big wheel. Our solar system is about 25,000 light years from the center of the system, and most objects in this traffic lane move at about 134 miles a second. Traffic lanes nearer the rim move at perhaps 126 miles a second.
This means that traffic in lanes near the center is forever catching up and passing us, while traffic in the outer lanes is always falling behind. Our solar system is in one of several starry arms that spiral out from the center of the milky way, and these spiraling arms trail behind the fast spinning center of the system. We are about 100 light years north of the milky way's equator, and viewed from this ang1e, the vast system rotates in a clockwise direction.
We cannot observe the rotation of the milky way with our eyes alone. But the telescope and the spectroscope indicate that all the stars seem to be moving toward or away from us. Those in the center lanes are overtaking and passing us, while we are overtaking and passing those in the slower outer lanes. Recently, the radio telescope has shown that masses of cloudy hydrogen also rotate with the milky way and follow the same traffic laws as do the stars.